Saturation-dip measurements for the stretching band of have been systematically carried out with a -laser–microwave-sideband spectrometer operating on low- and high- P-branch laser lines. Frequencies of nearly 500 spectral lines, including overlapped and doublet lines unresolved in dense Doppler-limited spectra, have been measured with a resolution of and absolute accuracy of the order of . Over 200 frequency combination loops have been formed from the present and previous sub-Doppler observations, unambiguously confirming the infrared transition assignments, and refined term values have been determined for 623 excited vibrational levels. These results constitute a substantial database of high-accuracy frequency reference standards for in the region, with applications in frequency calibration, in detailed studies of the complicated methanol intermode vibrational interactions, and in the interpretation of optically pumped far-infrared laser emission.
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